This invention relates to the switching of electromagnetic signals of millimeter wavelength and, more particularly, to the construction of a switch of multiple switching arms extending from a multiply-tapped transmission line configured to encircle a driver of the switching arms, thereby providing a switch architecture suitable for construction in a monolithic microwave integrated circuit (MMIC) chip.
Electronic signal processing, such as may be found in radar and in communication systems, may include a switching of signals from one terminal selectively to any one of a multiplicity of terminals. Such switching has been accomplished by mechanical stepping switches and by electronic switching circuits, both of which are physically large as compared to circuit component parts found in MMIC. Of particular interest herein is the capacity to switch millimeter-wave signals by use of circuitry compatible in physical size with an MMIC chip.
A problem arises in that circuitry employed for lower frequency signals is generally too large to fit within the confines of an MMIC chip. Attempts to produce selective, or N-way, switches with multiple output ports, or input ports, has resulted in geometry wherein connecting lines from a common node to the ports (a star configuration) are so close together, in the vicinity of the common node, as to introduce excessive parasitic capacitance which impairs signal transmission, as well as reducing isolation among respective ones of the ports which have been switched off. Attempts to reduce cross talk by cascading several switches, wherein one two-way switch feeds two further two-way switches, results in a circuit layout which is excessively large for MMIC chips, particularly upon inclusion of a suitable driver for the switches.